A novel virus that requires aggressive treatment to be survivable would quickly get out of hand. FTFA: "The men recovered but suffered serious illness that required hospital care and weeks of convalescence. Symptoms included fever, severe fatigue, headache and nausea. Their platelet counts plummeted, but even though platelets are necessary for blood clotting, the men didn't suffer abnormal bleeding."

We haven't had a need to triage patients in a long time. A wide spread outbreak would mean that some poor bastard would have to decides who gets a hospital bed, and who gets sent home to die. I'm going to guess the suicide rates among those who have to make those kinds of decisions would be quite high in the years after the outbreak.